The invention concerns a method and apparatus for determining the position of a wheel mounted on a motor vehicle.
A method of determining the position of a wheel mounted on a vehicle, wherein at least two diametrally disposed targets on the wheel which are associated with a given wheel position angle are irradiated from a transmitter, and the beams reflected by the target locations on the wheel are received by a receiver and wherein the beam transit times from emission to reception are measured, and an apparaus for carrying out such a method, are to be found in EP 0 581 990 A1. In that arrangement, light transmitting and receiving means are disposed on a rotary disk which, during a measurement procedure, is rotated about an axis which coincides with the axis of the wheel whose position is to be determined, in such a way that various points on the wheel are irradiated by the transmitted light, and the light reflected at such points is received again. In that procedure, the transit times of the beams associated with the respective irradiation points on the wheel are measured and recorded in an approximately sinusoidal curve. The irradiation points which are at 0xc2x0 and 180xc2x0 respectively afford a measurement value in respect of the track of the wheel while the irradiation points which are disposed at 90xc2x0 and 270xc2x0 respectively afford a measurement value in respect of wheel camber.
EP 0 280 941 B1 discloses projecting a geometrically structured light pattern on to the wheel whose position is to be determined, receiving that reflected light pattern as an image and using the geometrical shape of the received image to determine the relative position of the surface of the wheel in three-dimensional space and to ascertain therefrom the predetermined orientation characteristic of the wheel. In that procedure the position of the wheel on the vehicle is determined from the geometrical data of the received image, using known position-determining means, as are to be found in U.S. Pat. No. 4,111,557 and German laid-open application (DE-OS) No 25 14 930.
An object of the present invention is to provide a method of determining the position of a wheel mounted on a motor vehicle, in which the position of the wheel mounted on the motor vehicle can be determined irrespective of the optical image reproduction of the light pattern which is projected on to the wheel.
Another object of the present invention is to provide a method of determining the position of a wheel mounted on a motor vehicle, which can afford reliable and accurate measurement results while involving an operating procedure that is simple to carry into effect.
Still another object of the present invention is to provide a method of determining the position of a wheel mounted on a motor vehicle, involving operational procedures that can be implemented by uncomplicated structure.
Still a further object of the present invention is to provide an apparatus for determining the position of a wheel mounted on a vehicle, which can give accurate measurement results while not involving an over-complicated structure.
In accordance with the principles of the present invention the foregoing and other objects are attained by a method of determining the position of a wheel mounted on a motor vehicle, wherein at least first and second diametral target locations on the wheel, which are associated with a given wheel position angle, are irradiated from a transmitter, and the beams reflected by the target locations on the wheel are received by a receiver. The beam transit times from emission to reception are measured. The at least first and second diametral target locations are irradiated from a given location with spatially predetermined irradiation and reflection directions, and the reflected beams are received at a given location. The wheel position angle is determined from the given positions of the transmitter and the receiver, the predetermined irradiation and reflection directions, and the measured beam transit times.
In the apparatus aspect, the foregoing and other objects of the invention are attained by an apparatus for determining the position of a wheel mounted on a vehicle, comprising a transmitter for emitting beams towards at least first and second target locations on the wheel, which are associated with a wheel angle position. The apparatus includes a receiver for receiving the beams reflected by the target locations, a time measuring means for measuring the beam transit times from emission to reception and an evaluation means for evaluating the measurement values, thereby to determine the position of the wheel. The transmitter and the receiver are arranged at given positions and the transmitter emits first and second beams on to diametral target locations involving a given spatial orientation. The evaluation means is operable to determine the wheel position angle from the positions of the transmitter and the receiver, the directions of the beams and the beam transit times.
It will be seen therefore that, to determine the position of a wheel mounted on a motor vehicle, at least two target locations on the wheel are irradiated from a respective given location which is stationary at least during the measuring procedure and which thus constitutes a transmitter. The beams are reflected by the target locations and received at a respective given location which is stationary at least during the measuring procedure and which thus constitutes the receiver. The wheel position is determined from the measurement values which are obtained in that way. The signals associated with the respective target locations are emitted at given moments in time and the periods of time from emission to reception of the signals which are reflected at the respective target locations are measured. The wheel position is ascertained from the measured periods of time, with the measuring device being in the form of a time measuring device for measuring the period from the moment of emission of the respective signal associated with a target location, to the moment of reception of that signal.
The signals involved are preferably signals which are emitted for a brief period of time and which are of a given signal shape so that an association is afforded as between the emitted signal and the received signal, for time measurement purposes. The radiation involved is preferably electromagnetic radiation which can be suitably reflected at the surface of the wheel in the region of the disk portion thereof and/or at the surface of the tire bead. The radiation can also be in the visible wavelength range.
At least first and second target locations which are at an angular spacing from each other about the axis of the wheel, on the wheel surface, are irradiated. For the purposes of ascertaining the camber of the wheel, for example target locations which are disposed on the wheel in diametral relationship in a vertical plane passing through the axis of the wheel can be irradiated. For the purposes of ascertaining the wheel tracking, target locations disposed in a horizontal plane passing through the axis of the wheel can be irradiated.
In order to arrive at a suitable association between the emitted and received signals for the purposes of time measurement, the signals can involve different signal sequences or different frequencies. It is also possible to transmit given codings with the carrier frequency, and to measure the time that the coding requires from the moment of emission to the moment of reception.
Further objects, features and advantages of the invention will be apparent from the following description of a preferred embodiment thereof.